The invention relates to control methods for operating a refrigeration system which maintains a temperature set point by heating and cooling cycles, and more specifically to methods for enhancing the heating cycles of such systems.
Refrigeration systems capable of operating in a heating and defrosting mode are known in the art. Exemplary patents in this regard are commonly assigned U.S. Pat. Nos. 4,850,197; 5,228,301; 5,408,836; 5,410,889; 5,465,586; 5,465,587; 5,477,695; and 5,598,718, the disclosures of which are incorporated by reference herein. Such refrigeration systems generally employ a refrigerant compressor that is typically driven by an internal combustion engine in transport refrigeration systems. The compressor is connected to a refrigeration circuit that generally comprises a condenser coil for condensing gaseous refrigerant into a liquid, and an evaporator assembly that includes an expansion valve for converting the liquid refrigerant back into a gas, and an evaporator coil that is thermally connected to a conditioned space, which may be a truck trailer.
To achieve heating and defrosting, these systems typically incorporate a three-way mode valve to divert hot, gaseous refrigerant around the expansion valve of the evaporator assembly and directly into the evaporator coil. This converts the evaporator coil into a heat radiating condenser for either defrosting or heating applications. Such systems employ heat exchangers for transferring additional heat to the gaseous refrigerant to enhance the efficiency of the heating cycle. This additional heat may be provided from sources such as the hot liquid coolant of the radiator system of the internal combustion engine used to drive the compressor.
The foregoing illustrates existing refrigeration systems. It would be advantageous to provide an alternative refrigeration system having enhanced heat outputs during heating cycles including the features more fully disclosed hereinafter.